Even now, parasitic protozoan infections are widely known mainly around tropical or subtropical regions, and can be exemplified by malaria, leishmaniasis, African trypanosomiasis (African sleeping sickness), American trypanosomiasis (Chaga's disease), lymphatic filariasis, and babesiosis. These infections can be classified into those infecting only humans, and zoonosis also infecting domestic livestocks or small animals, both leading to significant economic and social loss. Among these diseases, there are some diseases that do not have a therapeutic agent showing a sufficient effect, or some have problems such as emergence and diffusion of drug-resistant protozoa, or side effects of therapeutic agents. Therefore, an effective agent is awaited.
For example, Pentostam, which is a therapeutic agent for leishmania contains antimony atoms in the molecule, and therefore, antimony intoxication cannot be avoided as a treatment side effect. Melarsoprol which is used in the primary treatment of African trypanosomiasis (African sleeping sickness) contains arsenic atoms in the molecule, and there is a problem that arsenic intoxication occurs as a side effect. Further, some of these diseases show severe symptoms that make it impossible to lead a normal social life, or force a patient to be bedridden necessitating care, or develop lethal symptoms. Thus, early development of a chemotherapeutic agent is indispensable.
A compound shown by general formula (1) contained in a medicinal composition of the present invention is known as an antitumor agent having a high selectivity to cancer cells (for example, see EP527,494; Japanese Laid-Open Patent Application No. 5-117148; and U85,861,424), while the use as an agent for treating or preventing parasitic protozoan infection is not known. On the other hand, the present inventors showed that a rhodacianine compound shown by the following general formula (3) has a therapeutic effect to malaria and leishmaniasis (for example, see Japanese Laid-Open Patent Application No. 2000-191531; Japanese Laid-Open Patent Application No. 2003-034640; Japanese Laid-Open Patent Application No. 2003-034641; and Japanese Laid-Open Patent Application No. 2003-034642). However, the correlation between parasitic infection and effect of an agent has not been much clarified, and under such present circumstance, it is quite difficult to find out a structure of a compound effective to protozoan infections. In other words, it was not clear whether a compound shown by general formula 1 of the present invention has an effect on protozoan infection or not, and such effect was not predictable.
(wherein R7 and R9 each independently represent an alkyl group; R8 represents an alkyl group, aryl group or heterocyclic group; C and D each independently represents an atom group necessary for forming a 5- or 6-membered heterocycle; P represents a physiologically acceptable anion; a represents an integer of 0 to 2, necessary to make the electric charge of the whole molecule 0; b represents 0 or 1.)    Patent document 1: EP 527,494    Patent document 2: Japanese Laid-Open Patent Application No. 5-117148    Patent document 3: U.S. Pat. No. 5,861,424    Patent document 4: Japanese Laid-Open Patent Application No. 2000-191531    Patent document 5: Japanese Laid-Open Patent Application No. 2003-034640    Patent document 6: Japanese Laid-Open Patent Application No. 2003-034641    Patent document 7: Japanese Laid-Open Patent Application No. 2003-034642